1. Position oven racks in upper and lower thirds of oven and preheat to 500°.
2. Pat roast dry and sprinkle all over with 1/2 teaspoon salt and 1/2 teaspoon pepper.
3. Place in roasting pan, fat side up. Insert leave-in thermometer into the center of meat. Cook in lower third of oven for 20 minutes.
4. Toss carrots with oil, water, cumin, and remaining salt and pepper. Arrange in an even layer in a large baking dish.
5. After beef has roasted 20 minutes, turn oven down to 325° and place carrots in upper third of oven. Roast carrots until tender and continue roasting beef until thermometer registers 125° (35-40 minutes). Transfer roast to a cutting board; let stand, uncovered, 10-15 minutes. (Make sure internal temp rises to 130° for medium-rare.)
6. Remove carrots from oven and sprinkle with balsamic, shaking pan to distribute vinegar. Thinly slice meat across the grain. Sprinkle parsley over carrots, and serve alongside beef.